This invention relates to a method for producing a bondable molded part according to the definition of the species of Claim 1. Such molded parts, e.g., components in automotive engineering, are produced by bonding two-sided adhesive tape to a base body. The outside of the adhesive tape applied to the base body is covered with a removable film. To attach the part to a housing, for example, the film is pulled off and the part is pressed in the intended location with the adhesive outside of the adhesive tape.
Fastening a part by means of two-sided adhesive tape has some important advantages in comparison with conventional fastening means, e.g., fastening screws, because rapid assembly is possible without requiring additional elements and it takes up very little space. Pressure-sensitive adhesives having an improved adhesive power are known and thus also permit good fastening of parts with appropriate pressure-sensitive adhesive tape accordingly. In the case of glass-filled or foamed adhesive tape with a higher density (usually 0.4-1 mm [sic]), permanent bonding of materials having different thermal expansion coefficients, e.g., aluminum plastic are possible. However, one disadvantage is that adhesives having a high viscosity and adhesive strength are difficult to process. And adhesive must be produced under protective gas and/or in the absence of oxygen. Adhesive tape with a high adhesive power produced in this way is therefore comparatively expensive.
The state of the art in the field of pressure-sensitive adhesives is described, for example, by I. Benedek, L. J. Heyman, “Pressure Sensitive Adhesive Technology,” Marcel Decker Inc., 1st edition, 1997. Basic polymers which are used as precursors of modern adhesives include mainly polyacrylates, natural and synthetic rubbers, polyesters, polychloroprene, polyisobutenes, polyvinyl ethers, polyurethanes and polysiloxanes, which are mixed with additives such as resins, plasticizers, fillers and stabilizers. In addition, applying the adhesive tape is complicated because the adhesive tape must be cut out or punched. Another disadvantage is that it is difficult to apply such adhesive tape to uneven or spherical surfaces.
WO 95/21734 discloses a bondable molded part made of plastic and a method for producing this molded part. The bondable molded part has an integrated adhesive part of a hot-melt adhesive. The adhesive part is produced in an injection mold in a separate step. The molded part is then cast onto the adhesive part, forming a flow seam. The adhesive part of the bondable molded part produced in this way is hard at ambient temperature and must be heated, e.g., by heat radiation, before the effective bonding operation. The required previous heating of the hot-melt adhesive before the effective bonding operation is complicated or even impossible for many applications.
European Patent 0 767 040 A relates to a method of bonding to a solid body. In this method an open cavity is sealed with the solid body and the adhesive is integrally molded on the body. The cavity is then filled completely with the adhesive. The adhesive is converted to a non-flowing material and finally removed from the mold. Closing a cavity with a part made of plastic is difficult and the high pressures used in injection molding processes in the usual way are impossible here. In addition, because of the sealing and supporting border, the entire surface up to the edge cannot be provided with adhesive.
Japanese Patent 57 059 737 A discloses a method and a device for producing a plastic part with an adhesive layer. In an extrusion mold, the plastic part is extruded through a slot and at the same time the adhesive is extruded and bonded to the plastic part. However, only films can be produced by this method.
Japanese Patent 63 31 28 18 A discloses a method in which a body is provided with an adhesive layer of a hot-melt adhesive to which metal powder is added. For bonding the body, the adhesive layer is heated by induction. It is complicated to heat an adhesive layer before bonding and in many cases it is not even possible.